The field of this invention is jet propulsion apparatus and methods. More particularly, this invention relates to jet propulsion apparatus of the turbofan type, and associated methods.
Modern aircraft are called upon to fulfill a wide variety of so-called mission requirements. Such mission requirements involve aspects of aircraft use such as short or normal runway takeoff; climb to cruise altitude under best-economy, noise-restricted, or maximum climb-rate conditions; economy cruise, and high speed cruise. In the case of military aircraft such mission requirements may also include aircraft loiter, high speed dash, and combat power settings at a variety of altitudes and with aircraft maneuvering required at both low and high Mach numbers with reliable engine operation despite rapid throttle manipulation; and with relatively low engine fuel consumption rates under all conditions.
Because of the wide variety of aircraft mission requirements, it is desirable to utilize a turbofan type of engine in order to secure the lowest possible engine fuel consumption rates. However, a turbofan engine has both a core engine exhaust duct and a fan bypass duct which each require a particular variation in discharge area and pressure ratio at the engine exhaust nozzle under varying engine operating conditions. Such a variation of discharge areas and pressure ratios is necessary in order to provide an appropriate bypass ratio for the engine under varying conditions to obtain best engine operating efficiency and reliability.
In view of the complex exhaust nozzle requirements of a turbofan engine under varying mission requirements, conventional turbofan engines have utilized a variety of complex nozzle schemes including multiple annular arrays of circumferentially overlappling leaves cooperating to define fan bypass, core engine exhaust, and nozzle throat areas which are variable by radial movement of the leaves. Other conventional nozzle schemes employ one or more arrays of movable leaves in conjunction with an axially translatable cowl section or plug member cooperating with the leaves to define variable fluid flow areas. All such conventional nozzles known to the applicant are structurally complex and require coordinate movement of a multiplicity of their components parts in order to achieve the objective for which they are provided. The structural complexity of such conventional turbofan exhaust nozzles causes them to be prone to wear, jamming and other failures. Further, such exhaust nozzle complexity requires equally complex nozzle actuation systems. Similarly, complex control systems are required to sense engine and aircraft operating paramaters and to control the nozzle actuator systems accordingly. All in all, designers of conventional turbofan engines with variable exhaust nozzles have responded to the complex exhaust nozzle requirements of the turbofan type engine with costly, failure-prone and structurally complex exhaust nozzle structures and methods.
U.S. Pat. Nos. 2,570,629; 2,928,235; 3,068,644; 3,261,164; 3,447,325; 3,670,964; and 3,841,091, illustrate subject matter believed by the applicant to be relevant to the subject invention.